The present invention relates to compositions for surface treatments for substrates, such as paper and polymeric plastic material used for ink jet printing, as well as methods for making the printing substrates, the treated printing substrate itself, methods of enhancing ink jet printing, and ink jet printed printing substrates.
In today's commercial, business, office and home environments, paper is commonly used for multiple purposes, such as reprographic copying, laser printing, ink jet printing, and the like. Specialty papers have been developed for each type of application, but as a practical matter, a multipurpose paper suitable for all such uses is desirable. Of the above-indcated uses, perhaps ink jet printing has the most demanding requirements, since the ink is printed wet and must provide good print quality and dry quickly, properties which are often difficult to achieve together.
Much of the paper intended for ink jet printing is coated with various types of special coatings, typically a layer of water soluble polymer and silica and other insoluble fillers, that makes the paper very expensive, especially in consideration of the desire and tendency to use the paper for other general office purposes, such as copying and laser printing. A typical cost per page of such paper is about $0.10. By comparison, uncoated paper, such as copy paper, generally sells for less than $0.01 per page.
Ink jet printing has been practiced commercially only in recent years. Desk top ink jet printing is an even more recent development. Most ink jet printing inks, both black ink and colored inks, are dye-based inks. Use of black pigmented inks in desk top ink jet printing is relatively new, dating from the introduction of Hewlett Packard's DeskJet.RTM. 660C printer in 1994. Desk top ink jet printing with pigmented inks other than black, e.g., pigment-based colored inks, has yet to become commercially available, but is expected to become comercially available in the near future.
Paper is made with and/or surface treated with sizing agents primarily to prevent excess penetration, wicking or spread of water or ink. Many different types of nonreactive and reactive sizing agents are well known in the papermaking industry. Paper typically made under acidic paper making conditions, referred to as acid paper, is ususally sized with well-known rosin-derived sizing agents (referred to herein as "dispersed rosin sizing agents"), a nonreactive sizing agent. Some papers made under neutral and alkaline paper making conditions may also be sized with dispersed rosin sizing agents. The most common sizing agents for fine paper made under alkaline conditions, referred to as alkaline paper, are alkenyl succinic anhydride (ASA) and alkyl ketene dimer (AKD). Another class of sizing agents useful for sizing fine paper includes ketene dimers and multimers that are liquid at room temperature, such as alkenyl ketene dimers and multimers. These are reactive sizing agents, since they have a reactive functional group that covalently bonds to cellulose fiber in the paper and hydrophobic tails that are oriented away from the fiber. The nature and orientation of these hydrophobic tails cause the fiber to repel water.
The growing popularity of ink jet printers has also focused attention on the sizing requirements for paper intended for this end use application.
The following ink jet print characteristics relating to print quality have been identified by manufacturers of ink jet printers as being important to high quality ink jet printing, many of which are affected by the type and treatment of paper or other substrate to which the ink is applied.
OPTICAL DENSITY: Color intensity as measured by the change in reflectance (OD=log.sub.10 (I.sub.i /I.sub.r) where I.sub.i and I.sub.r =Incident and reflected light intensities, respectively), where high optical density is desired.
SHOW THROUGH: Color intensity of an image that is observed from the back side of the sheet, which can be measured by optical density.
SPECKLED SHOW THROUGH: Often on the back side of a printed image there is a speckled appearance as ink finds its way through pinholes or areas of poor formation.
LINE GROWTH (BLEED) (FEATHERING): The final printed size features versus the initial printed size, which can be seen as lost resolution. It occurs in both single color printing and when colors are printed next to and on top of each other.
EDGE ROUGHNESS (SOMETIMES CALLED FEATHERING): A rough versus smooth appearance of edges as ink spreads unevenly away from the printed area. It occurs in both single color printing and when colors are printed next to or on top of each other.
WICKING: Observed as long spikes of ink extending from printed areas such as when ink runs along a single fiber at the surface of the paper.
MOTTLE: Unevenness of the print optical density in a solid printed area.
BRONZING: An appearance in black printed areas of a bronze sheen (reddish tint).
COLOR INDEX: The hue or shade of the printed colors or combined colors. In addition, with a composite black print (made with cyan, magenta, and yellow), there is often a greenish tint.
DRY TIME: The time it takes for the ink to dry such that it will not smear or transfer to other surfaces.
CASCADING: Lines of low print density that occur between passes of the print head, which is usually observed on some very highly sized papers.
INSUFFICIENT DOT GAIN: Similar to cascading but shows up as a white area visible around dots of ink in a solid print area because they have not spread enough. The effect is to lower optical density.
MISTING: Very small spots visible around the edges of printed areas that come from where very small drops (mist) of ink have sprayed out from the main print droplet.
It has been known to coat paper used as photocopy paper with materials that increase its conductivity, e.g., treating the paper so that the paper has a hygroscopic inorganic salt throughout its body structure as disclosed by Uber et al. in U.S. Pat. No. 3,116,147; by coating with inorganic salt-resin coatings as described by Cheng in U.S. Pat. No. 3,615,403; by surface treating with a binder like starch and a sulfate salt as described by Green, Jr. et al. in U.S. Pat. No. 3,884,685; or by surface treating with microencapsulated salts as described by Geer in U.S. Pat. No. 4,020,210.
Calcium carbonate is often added to paper as a dispersed filler. Calcium carbonate has the disadvantage of being a relatively insoluble particulate solid that requires dispersing in aqueous systems. The presence of fillers such as calcium carbonate can lead to increased wear of equipment parts during paper manufacture and end-use applications.
Calcium chloride in high concentrations with a reactive sizing agent have been added to paper, as a first of two coatings, the second of which includes calcium carbonate, potassium silicate and carboxymethylcellulose, to control burn characteristics such as in cigarettes, as disclosed by Kasbo et al. in U.S. Pat. No. 5,170,807, but such paper is not suitable for ink jet printing, and such high concentrations of calcium chloride are not suitable for preparing a paper used for printing.
Aluminum sulfate (alum) is a common additive to many paper machines, generally being added at the wet end of a paper machine. Alum is added to rosin sizing dispersions, used as internal sizes in paper making, and the alum level in the rosin sizing dispersion may be as high as 66% of the solids. Alum is dissolved at a low pH to give cationic aluminum species. Alum will form non-cationic species at a typical size press pH of 8.
Calcium chloride has been added to paper for milk carton applications. Such paper has a high basis weight about 3 to 5 times greater than normal copy paper and is coated with wax.
Sizing compositions particularly for sizing paper used in products with superior alkali metal or aluminum liquid storage properties include a metal salt selected from zirconium, hafnium, titanium and mixtures thereof, as described in Pandian et al. U.S. Pat. No. 5,472,485.
Sizing dispersions containing storage stabilizing amounts of water-soluble alkali metal or aluminum inorganic salts are described in International Patent Publication WO 96/35841 of Eka Chemicals AB, useful as internal sizes or surface sizes for paper, board and cardboard.
Paper has been treated with relatively high concentrations 0.5-5% of deliquescent salt such that the paper, used as a base material for a resin-coated laminate, does not have wavy deformations at the edges when the paper is coated on both surfaces with synthetic resin films, as described by Minagawa et al. in U.S. Pat. No. 4,110,155.
Paper suitable for ink jet printing with dye-based inks is described by Kuroyama et al. in U.S. Pat. No. 5,522,968, Suzuki et al. in U.S. Pat. No. 5,620,793 and Sakaki et al. in U.S. Pat. Nos. 5,266,383 and 5,182,175.
A method and equipment for ink jet printing with pigmented ink is described by Kashiwazaki et al. in U.S. Pat. No. 5,640,187. As is evident from the disclosures of Kashiwazaki et al., a need exists for quality ink jet printing performance without resorting to the use of specialty coated paper.
The disclosures of all of the patents, published applications and other publications identified herein are hereby incorporated herein by reference.